# pg_appendonly 

The `pg_appendonly` table contains information about the storage options and other characteristics of append-optimized tables.

|column|type|references|description|
|------|----|----------|-----------|
|`relid`|oid| |The table object identifier \(OID\) of the compressed table.|
|`blocksize`|integer| |Block size used for compression of append-optimized tables. Valid values are 8K - 2M. Default is `32K`.|
|`safefswritesize`|integer| |Minimum size for safe write operations to append-optimized tables in a non-mature file system. Commonly set to a multiple of the extent size of the file system; for example, Linux ext3 is 4096 bytes, so a value of 32768 is commonly used.|
|`compresslevel`|smallint| |The compression level, with compression ratio increasing from 1 to 19. When `quicklz`<sup>1</sup> is specified for compresstype, valid values are 1 or 3. With `zlib` specified, valid values are 1-9. When `zstd` is specified, valid values are 1-19.|
|`majorversion`|smallint| |The major version number of the pg\_appendonly table.|
|`minorversion`|smallint| |The minor version number of the pg\_appendonly table.|
|`checksum`|boolean| |A checksum value that is stored to compare the state of a block of data at compression time and at scan time to ensure data integrity.|
|`compresstype`|text| |Type of compression used to compress append-optimized tables. Valid values are:<br/><br/>-   `none` \(no compression\)<br/><br/>-   `rle_type` \(run-length encoding compression\)<br/><br/>-   `zlib` \(gzip compression\)<br/><br/>-   `zstd` \(Zstandard compression\)<br/><br/>-   `quicklz`|
|`columnstore`|boolean| |`1` for column-oriented storage, `0` for row-oriented storage.|
|`segrelid`|oid| |Table on-disk segment file id.|
|`segidxid`|oid| |Index on-disk segment file id.|
|`blkdirrelid`|oid| |Block used for on-disk column-oriented table file.|
|`blkdiridxid`|oid| |Block used for on-disk column-oriented index file.|
|`visimaprelid`|oid| |Visibility map for the table.|
|`visimapidxid`|oid| |B-tree index on the visibility map.|

> **Note** QuickLZ compression is available only in the commercial release of VMware Greenplum. Support for the QuickLZ compression algorithm is deprecated and will be removed in the next major release of VMware Greenplum.

**Parent topic:** [System Catalogs Definitions](../system_catalogs/catalog_ref-html.html)

